Lockout mechanism systems for vehicle shifters wherein the brakes of the vehicle have to be applied before the shifter can be shifted from out of park to drive positions are common. Many different mechanisms have been devised for such purpose. One such mechanism is illustrated in FIG. 9 wherein a detent plate 100 is provided with a plurality of notches for positioning the shifting lever and releasably holding it in various positions. This is conventionally accomplished by providing the lever with a pawl 101 movable into any one of the numerous notches such as the notch "P" for the park position, the notch "R" for the reverse position, "N" for the neutral position, and "D, " "D.sub.2," "D.sub.1 " for various drive positions. In order to lock the pawl 101 in the notch "P" (the park position), a lockout arm 103 is provided. The lockout arm is pivotally mounted on the pin 104 at one end and at the other end a notch 105 is provided to capture the pawl 101. A spring 106 is attached to the base 107 at one of its ends and at the other of its ends is attached to a flange 108 extending from the lockout arm 103. A locking member or pin 109 is provided to lock the lockout arm 103 in lock position as disclosed by solid lines in FIG. 9. The pin 109 is forced in a direction orthogonal to the lockout arm 103 and when in the position as disclosed in FIG. 9, engages the edge 110 to hold pin 101 in the "P" notch, that is in the Park position. The pin 109 is withdrawn to a distended position when the brake of the vehicle is applied. As a result, the pawl 101 actuated at the top end of the shift lever (not shown in FIG. 9) can push the lockout arm 103 downwardly to permit the escape of pawl 101 from the "P" notch and be shifted to one of the other gear positions all of which will be explained in greater detail hereinafter.
The problem with this mechanism is that when the lockout arm 103 is pivoted downwardly to release the pawl 101, the pin 109 has a constant force exerted on it forcing it against the back face of the lockout arm 103. So long as it is in that position as disclosed by the dotted lines, the pawl 101 can enter the notch 105 after which it can move into the notch "P." However, although the spring 106 will tend to hold the lockout arm 103 in the dotted position wherein the pawl can reenter into the "P" notch, a sudden jolt caused by a bump in a road or other disturbances may cause the lockout arm 103 to jump upwardly into the position as disclosed in solid lines, in which position the force on the pin 109 forces it to extended position which locks the lockout arm in lock position. In this position, the pawl 101 located in any one of the other notches is blocked from reentering the park "P" position as illustrated by the pawl 101 shown in dotted lines.